Figure 17.2: Cryptic Species Look Alike but Do Not Interbreed These two species of gray treefrogs (Hyla versicolor and H. chrysoscelis) cannot be distinguished by their external morphology, but they do not interbreed even when they occupy the same geographic range. H. versicolor is a tetraploid species, whereas H. chrysoscelis is diploid. Although they look alike, the males have distinctive mating calls, and based on these calls, the females recognize and mate with males of their own species.